I too think the concept of a Sith Jawa is a neat idea, lol
My only thoughts that spring to mind is when I think of a Jawa that's gone over to the dark side, I see his face still being black (shadowed) and maybe adding another type of cloak in addition to his regular tatooinian (sp?) attire. Can't go wrong with layering his cloaks:)
Also, since Sith are big on technology, I'd also see maybe some sort of advanced breathing filter or even a larger breathing apparatus that was directly implanted onto/into him.
In any case, it's a really cool idea, AND nice work on your clones!